The Air Force canceled expensive upgrades to 196 F-15C fighters last year as it hammered out a plan to retire the jets, according to a recently declassified report.

The fighters were supposed to get new electronic warfare equipment known as the Eagle Passive/Active Warning and Survivability System, said the Department of Defense Inspector General report declassified on May 21.

The Air Force had planned to spend $3.4 billion installing the gear on all F-15Cs and 217 F-15Es, giving them “electronic warfare capabilities to detect and identify air and ground threats, employ counter-measures, and jam enemy radar signals,” the report said.

However, in February 2017 the service ordered a 47 percent cut to the number of jets getting the new equipment, which replaces a dated 1970s electronic warfare package and is designed to increase the F-15C’s survivability in a contested environment.

The IG report outlined a timeline for retiring the jets, but many details were redacted.

Before that happens, Air Force officials must brief Congress on options to replace F-15C Air Superiority Mission capabilities, validate whether upgraded F-16s are a viable replacement, and identify transition plans for locations that support F-15C aircraft, personnel, operations or maintenance activities, the report said.

Officials from the service told lawmakers in March 2017 that they would consider retiring the aircraft during budget planning for the 2019 fiscal year.

If Congress doesn’t approve the retirement, the Air Force will restore funds to install the electronic warfare gear on F-15Cs based on mission requirements, an Air Force official said in the report.